The use of hand operated pointing devices to control the position of a cursor on a computer display has become extremely widespread. The most popular of such navigation devices is the mouse. Recently, in computer mouses being commercialized in the United States, the mechanical ball that partially protrudes through the underside of the mouse has been replaced with an optical laser tracking device to avoid failures due to lint build-up and mechanical wear associated with the ball. See U.S. Pat. No. 6,281,882 granted Aug. 28, 2001 to Gordon et al., assigned to Agilent Technologies, Inc., and entitled PROXIMITY DETECTOR FOR A SEEING EYE MOUSE.
Small track balls, drag pads, and strain sensing sticks have been used on lap top computers since they are often used in environments where a drag surface for a mouse is not available and it is impractical to have a cord connecting the lap top to the pointing device. In so-called personal digital assistants (PDAs) a stylus is often used to select icons and write cryptic symbols onto a tiny touch screen that are interpreted by character recognition software.
As PDAs, cell phones, pagers, pocket PCs, music players, digital cameras, game controllers, presentation pointers and other portable hand held electronic apparatus gain popularity, there is a need for an improved pointing device that is compact, accurate, durable and easy to operate. The use of a pointing device on a portable hand held electronic apparatus enables multidirectional cursor control for menu selection, web browsing and other user controlled functions. One example of a suitable pointing device for this application is disclosed in U.S. Pat. No. 6,057,540 granted May 2, 2000 to Gordon et al., assigned to Hewlett-Packard Company, and entitled MOUSELESS OPTICAL AND POSITION TRANSLATION TYPE SCREEN POINTER CONTROL FOR A COMPUTER SYSTEM. A user's finger tip is moved over the distal end of a transparent rod lens which provides an imaging surface. Light from an LED adjacent the proximal end of the rod lens illuminates the finger tip. A plurality of photo detectors in a movement sensor adjacent the proximal end of the rod receive light reflected from the finger tip which is focused on the detectors by another lens also on the proximal end of the rod lens. The movement sensor generates pixelized representations comprising a reference array and shifted versions thereof that are used to generate navigation signals indicative of motion in X and Y axes.
It has been discovered that a pointing device that relies on the motion of a digit across an imaging surface can produce annoying inaccuracies due to jagged and/or non-uniform cursor movement. This appears to be due to the fact that the surface of a finger tip or other digit is not rigid like a desktop or mouse pad. The surface of the finger tip lags and whips as it is dragged across the rigid, stationary imaging surface formed by the distal end of the rod lens.
Another shortcoming of a pointing device that relies on the motion of a digit across an imaging surface is that multiple finger strokes may be necessary to move the cursor from one side of the display to the other. This drawback is similar to that encountered with drag pads incorporated into lap top computers.
Still another shortcoming of a pointing device that relies on the motion of a digit across an imaging surface is that it is sometimes difficult to make the transition between cursor movement and action selection, for example at a menu or URL link. A finger lift-up motion followed by a finger put-down motion to accomplish a click can lead to spurious cursor motion and ineffective user commands.